1. Field of the Invention
The present invention relates to an improved process for the preparation of Type Y zeolites.
2. Description of the Prior Art
Type Y zeolites are well known crystalline zeolites having the same structure as natural faujasite or Type X zeolites, but a different chemical composition. U.S. Pat. No. 3,130,007 describes the characteristic compositions of Type Y zeolites and reports their X-ray powder diffraction data.
Various processes for the preparation of Type Y zeolites are known to the art. Said U.S. Pat. No. 3,130,007, for example, features a process comprising the following steps:
(1) preparing an aqueous mixture of given proportions from a sodium aluminate and a silica source selected from among colloidal silica sols, silica gels, silicic acid, sodium silicate, and amorphous solid silicas;
(2) whereupon the reaction mixture is immediately gelled, and then digesting same at ambient temperature for a period of time ranging from 16 to 40 hours;
(3) next heating the reaction mixture to a temperature of about 100.degree. C., without agitation (to avoid formation of competing zeolites), until Type Y zeolite crystals are formed; and
(4) finally, separating the product Type Y zeolite crystals from the mother liquor, through filtration. The crystals are then washed and dried.
The process described in the aforenoted U.S. Pat. No. 3,130,007 has the essential disadvantage of requiring a long period of digestion at ambient temperature and equally long crystallization periods. Indeed, according to Example 14 of this patent, the digestion was for 28 hours and the crystallization was for 48 hours.
And in French Pat. No. 1,475,167 is described a process for the preparation of Type Y zeolites comprising the following steps:
(1) preparing an aqueous reaction mixture of a soluble aluminum compound, a siliceous component having a degree of activity of at least 100 units (called an "active silicate"), and colloidal silica;
(2) whereupon the reaction mixture is immediately gelled, and then crystallizing Type Y zeolite crystals by aging same at a temperature of from 20.degree. to 120.degree. C. under agitation; and
(3) separating the product Type Y zeolite crystals therefrom, and washing and drying same.
The process described in said French Pat. No. 1,475,167 has the essential drawback of requiring the use of a very special "active silicate" that severely limits its attractiveness from a manufacturing point of view. To use such process, it is moreover necessary to verify the "activity" of the silicate beforehand. Cf. U.S. Pat. No. 4,164,551.